In an internal combustion engine provided with a supercharger, for example, a turbocharger, a waste gate valve (hereinafter mainly abbreviated as WGV) for opening/closing an exhaust bypass passage, which is arranged so as to bypass a flow passage of exhaust gas flowing into a turbine, is provided. Through adjustment of a flow rate of the exhaust gas flowing through the exhaust bypass passage in accordance with the opening degree of the WGV, output of the turbine and a compressor rotating integrally with the turbine is adjusted, and a pressure of intake air compressed by the compressor is controlled to be a desired supercharging pressure.
In the following, a description is given while referring to reference numerals of FIG. 1.
In recent years, there has been known a control device 50 employing an electric actuator 34 incorporating a motor to allow an opening degree of a WGV 31 to be freely set. Out of the documents disclosing such a control device, there is particularly a document disclosing a control device configured to determine a target opening degree of the WGV 31 for acquiring an optimal supercharging pressure in accordance with an operation state of an internal combustion engine 10, and to apply feedback control so that the target opening degree of the WGV 31 and an actual opening degree of the WGV 31 detected by a position sensor 53 match each other (e.g., refer to Patent Literature 1).
The target opening degree of the WGV 31 is determined based on various types of information indicating the operation state of the internal combustion engine. For example, in the control device disclosed in Patent Literature 1, the target opening degree of the WGV 31 is determined based on map data of a rotation speed NE and a throttle opening degree TA of the internal combustion engine.
A position sensor 53 is configured to detect a position of the actuator 34, and output, as an electric signal, an operation position of the WGV 31, which opens/closes in association with the actuator 34. For example, the position sensor 53 having an output characteristic shown in FIG. 5, in which an operation position AOP of the actuator 34 is assigned to the horizontal axis and a position sensor output voltage Vs is assigned to the vertical axis, is adjusted and assembled so as to output Vs=Vmin when the WGV 31 fully closes the exhaust bypass passage 30, and the WGV opening degree Pv on this occasion is set to 0%.
Then, when the actuator 34 is moved from this position to an upper limit of an actuator control range ACR, the output voltage of the position sensor 53 is designed so as to increase by Vrng. Thus, the position sensor output voltage Vs becomes Vmin+Vrng=Vmax when the actuator 34 is moved to the upper limit of the control range ACR.
In other words, the output voltage Vs of the position sensor 53 ranges from Vmin to Vmin+Vrng in accordance with the operation position of the actuator 34, and when Vs=Vmin, the WGV opening degree Pv may be defined to be 0% (WGV 31 fully closed position CP), whereas when Vs=Vmax, the WGV opening degree Pv may be defined to be 100% (WGV 31 fully open position OP).
Thus, an actual opening degree Pv of the WGV 31 is acquired from the position sensor output voltage Vs in accordance with Expression (1).Pv=(Vs−Vmin)÷Vrng×100  Expression (1)where:                Pv: WGV opening degree (%)        Vs: Position sensor output voltage (V)        Vmin: Fully closed position (V)        Vmax: Fully open position (V)        Vrng=Vmax-Vmin: Output voltage range for the movement from the lower limit to the upper limit of the actuator control range        
The fully closed position CP of the WGV 31 may deviate as a result of an assembly tolerance when the WGV 31 and the actuator 34 are connected to each other, a thermal expansion or wear of members, or other causes. In consideration of the occurrence of the deviation, an operable range AOR of the actuator 34 is designed so as to be wider than the actuator control range ACR. The position sensor 53 is also configured to output a voltage of from a lowest voltage VL to a highest voltage VH, which are output voltages when the actuator 34 is at both ends of the operable range AOR.
Moreover, as a method of controlling the actuator 34 so that the opening degree of the WGV 31 matches the target opening degree, there is generally used feedback control of using proportional-integral calculation (PI) based on the target opening degree and the actual opening degree, calculation (PID) of combining the proportional-integral calculation with derivative calculation, or calculation of combining the proportional-integral calculation with feed-forward (FF) calculation. The feedback control is used to automatically correct the operation amount of the actuator 34 so that the target opening degree and the actual opening degree match each other even when a difference occurs between the target opening degree and the actual opening degree, thereby resolving the difference between the target opening degree and the actual opening degree.
FIG. 6A to FIG. 6F are time charts for illustrating an example of behaviors of a target opening degree and an actual opening degree of the WGV 31 and respective calculation results when the target opening degree is changed stepwise in accordance with feedback control in which the proportional-integral calculation is combined with the FF calculation. For the sake of a simple description, the derivative calculation is omitted.
FIG. 6A to FIG. 6F have the time as their horizontal axes in common, and have, as their vertical axes, respective calculation results of behaviors of a target opening degree Sv and an actual opening degree Pv, an integral term, a proportional term, an FF term, a feedback correction amount, and an actuator operation amount in the stated order from the top as waveform charts. Those calculation results are acquired in accordance with Expression (2) and Expression (3). As expressed by Expression (2), an actuator operation amount Mv[n] is acquired by adding a feedback correction amount ΔMv[n] to a previous value Mv[n−1] of an actuator operation amount Mv.
Moreover, as expressed by Expression (3), the feedback correction amount ΔMv[n] is acquired as a sum of three calculation terms of an integral term acquired by multiplying a difference between a target opening degree Sv[n] and an actual opening degree Pv[n] by an integral gain Ki, a proportional term acquired by multiplying a difference between a current value Pv[n] of the actual opening degree and a previous value Pv [n−1] of the actual opening degree by a proportional gain Kp, and an FF term acquired by multiplying a difference between a current value Sv[n] and a previous value Sv[n−1] of the target opening degree by an FF gain Kf.Mv[n]=Mv[n−1]+ΔMv[n]  Expression (2)where:                Mv[n]: Operation amount (current value)        Mv[n−1]: Operation amount (previous value)        ΔMv[n]: Feedback correction amount (current value)ΔMv[n]=(integral term)+(proportional term)+(FF term)==(Sv[n]−Pv[n])×Ki+(Pv[n]−Pv[n−1])×Kp+(Sv[n]−Sv[n−1])×Kf  Expression (3)where:        Sv[n]: Target opening degree (current value)        Sv[n−1]: Target opening degree (previous value)        Pv[n]: Actual opening degree (current value)        Pv[n−1]: Actual opening degree (previous value)        Ki: Integral gain        Kp: Proportional gain (Kp<0)        Kf: FF gain        [n] indicates a calculated value at the current control timing, and [n−1] indicates a calculated value at the previous control timing.        
In the above-mentioned feedback control, the integral term acts to resolve the steady difference between the target opening degree and the actual opening degree. The proportional term acts to decrease the operation amount given by the FF term in accordance with a degree of convergence of the difference between the target opening degree and the actual opening degree. The FF term acts to resolve the difference between the target opening degree and the actual opening degree occurring in accordance with a change amount of the target opening degree when the target opening degree changes.
The operation amount of the actuator 34 is corrected through use of the feedback correction amount, which is the sum of the integral term, the proportional term, and the FF term acquired in this way, and the control is applied so that the target opening degree and the actual opening degree of the WGV 31 match each other.
The fully closed position of the WGV 31 may deviate resulting from the assembly tolerance when the WGV 31 and the actuator 34 are connected to each other, the thermal expansion or wear of members, and other causes as described above. However, there arises such a problem that when the fully closed position of the WGV 31 deviates, even in a case where the target opening degree and the actual opening degree in terms of the control match each other, an actual flow rate of the exhaust gas flowing through the exhaust bypass passage 30 deviates, and consequently, the pressure of the intake air to be compressed by the compressor deviates from the desired supercharging pressure. Thus, in order to prevent controllability of the supercharging pressure from degrading, the fully closed position of the WGV opening degree needs to be learned in order to handle the degradation.
As a method of learning the fully closed position of the WGV opening degree, for example, the following method is employed. Specifically, a condition under which the output voltage of the position sensor 53 becomes the minimum value VL (refer to FIG. 5) as a result of an occurrence of a deviation of the fully closed position toward the lower limit side is recognized in advance by measurement or the like. Then, when an internal combustion engine required opening degree, which is determined based on the operation state of the internal combustion engine 10, is set to 0% (WGV 31 full closing), the target opening degree is replaced by an opening degree acquired by assigning the minimum value VL to Vs of Expression (1) in place of the internal combustion engine required opening degree, thereby carrying out the feedback control.
As a result, irrespective of the true fully closed position in the variation range, a state in which the WGV 31 is pressed against the operation position at which the exhaust bypass passage 30 is completely closed can be brought about.
Then, it is determined whether or not the actual opening degree no longer changes when the control is carried out toward the target opening degree converted based on the minimum value VL. Then, the actual position on this occasion is determined to be the true fully closed position, and the output voltage of the position sensor at that time is updated as a full closing learned position.
Referring to an operation time chart of the target opening degree and the actual opening degree when “full closing position learning” of the WGV opening degree illustrated in FIG. 7 is carried out, a description is given of this method. In this time chart, there is illustrated an example in which the time is assigned to the horizontal axis, and the position sensor output voltage Vs and the actual opening degree Pv of the WGV 31 converted in accordance with Expression (1) are assigned to the vertical axes.
In <Period A> of FIG. 7, the control device 50 currently recognizes the full closing learned position Vmin as 1.5 V. Moreover, when Vrng is 2 V (design value), the WGV opening degree Pv in <Period A> is acquired in accordance with Expression (4).Pv(%)=(Vs−Vmin)÷Vrng×100=(Vs−1.5)÷2×100  Exression (4)
Before a time t1 in <Period A>, an internal combustion engine required opening degree Seng is 100%, and the target opening degree is thus set to a position corresponding to Vs=3.5 V.
Then, at the time t1, the internal combustion engine required opening degree Seng (represented as the dotted line) changes from 100% to 0% (from 3.5 V to 1.5 V, which is calculated backward in terms of Vs in accordance with Expression (4)). Thus, the full closing learning control changes the target opening degree Sv from 0%, which is the internal combustion engine required opening degree Seng, to a full closing learning target opening degree Slrn, which is an opening degree when the position sensor output voltage becomes the minimum value VL due to the occurrence of the deviation toward the lower limit side of the fully closed position.
Assuming that VL=1.1, (VL−1.5)÷2×100=−20% is acquired in accordance with Expression (4), and the feedback control is applied to the actual opening degree Pv toward −20% in the control device 50.
When it is assumed that the true fully closed position deviates from the full closing learned position Vmin (=1.5 V) recognized by the control device 50 to the position corresponding to Vs=1.3 V, the feedback control is applied to the actual opening degree Pv of the WGV 31 toward −20% (position corresponding to Vs=1.1 V), which is the replaced target opening degree Slrn, but the actual opening degree Pv does not become equal to or less than −10% (Vs=1.3 V), and the opening degree of the WGV 31 stays at −10% after a time t2.
On this occasion, the WGV 31 is pressed against the position at which the exhaust bypass passage 30 is completely closed, and the control device 50 thus determines that the opening degree of WGV 31 stays at −10% while providing a protection period as a stop determination period ΔT. The reason for providing the stop determination period ΔT is to prevent a determination error in the learning of the true fully closed position, and is set in order to positively determine the state in which the WGV opening degree Pv does not move continues for ΔT, which is the predetermined period, through use of the output voltage Vs of the position sensor 53. Thus, the full closing learned position is not updated at a time t3 between the time t2 and a time t4, at which the stop determination period ΔT has not elapsed.
Then, at the time t4, the stop determination period ΔT has elapsed since the time t2, and the true fully closed position is thus determined to be Vs=1.3 V. The full closing learned position Vmin is then updated from 1.5 V to 1.3 V, and the full closing learning control is finished. Simultaneously, the internal combustion engine target opening degree Seng is also returned to 0%, which is the original internal combustion engine required opening degree, at the time t4.
As a result, after the time t4, the full closing learned position is corrected to Vmin=1.3 V, and the WGV opening degree Pv in <Period B> may now be acquired from Expression (5).Pv(%)=(Vs−Vmin)÷Vrng×100=(Vs−1.3)÷2×100  Expression (5)
The fully closed position of the WGV 31 is updated to the correct position by applying the full closing learning control described above. Thus, the flow rate of the exhaust gas flowing through the exhaust bypass passage 30 is prevented from deviating, and the degradation in the controllability of the supercharging pressure is thus avoided.